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Unread 04-17-2015, 05:50 PM   #1
seasoned_geek
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1990 XJ Cherokee 
 
Join Date: Oct 2014
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90 XJ electric fan not coming on all of the time

This is a sticky wicket.

90 Wagoneer Ltd. Basically the entire cooling system has been replaced within the past year. Radiator, electric fan, mechanical fan clutch, water pump, thermostat, coolant, temp sensor in radiator, relay, probably more parts which I cannot remember. Yes, I even put a brand new shroud around the mechanical fan.

If left to idle when 60+ degrees out, sometimes the electric fan will come on to stop the motor from overheating and sometimes electric fan doesn't come on so motor overheats.

Oh, this engine is relatively new. Well past the 5yr portion of the 100K warranty from PowerPro2000, but, barely 20K on the motor.

Yes, the radiator which is in it is a single core OEM replacement. I just ordered a 3-core tonight. That is only going to mask the problems (plural).

Problem 1: Shouldn't possibly be able to overheat idling on 60 degree day.
Problem 2: When engine gets warm electric fan _should_ always kick on.

I'm looking for answers to problem 2. After reading many many many posts in many places I'm pretty certain the heater valve (and possibly the core) are the answer to problem 1. Those are the only two components in the cooling system which haven't been replaced at least twice in the past 1.5 years.

Problem 2 is mighty )(*&^)(*&)ing annoying.

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Unread 04-19-2015, 09:21 AM   #2
Motorcharge
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1. Can you verify that it is actually overheating beyond simply seeing what the gauge reads? It's possible the sensor for the gauge is bad or that that portion of the instrument cluster isn't working properly anymore. Yes it's possible for it to overheat at idle regardless of the temperature outside, more or less.

2. It should kick on when the A/C compressor is on or at 210*. If it's not kicking on at 210 but does actually work the temp sensor for the computer may be bad.

There are two coolant temp sensors on the older Cherokees. The one on the thermostat housing is for the computer and then there's a second on on the very back of the cylinder head on the drivers side that reads for the gauge cluster.

If you're not getting any boil over or other signs that it's actually overheating then go get a cheap infrared laser thermometer and report back with actual temps. Read on the tstat housing and hoses. It's entirely possibly you're idling under 110 and the efan isn't kicking on because it's not supposed to but the dash gauge is completely wrong. I replaced the entire cooling system on my 92 only to find it was cooling properly and in the end the instrument cluster was bad (which I should have known since the battery and oil gauges didn't work).

Both sensors are cheap (under $10 iirc) and easy to replace. Engine needs to be cool for both though because they plug holes where coolant can come out if it's hot.
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Unread 04-19-2015, 09:44 AM   #3
Paradise XJ
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Originally Posted by Motorcharge View Post
There are two coolant temp sensors on the older Cherokees. The one on the thermostat housing is for the computer and then there's a second on on the very back of the cylinder head on the drivers side that reads for the gauge cluster.
There are actually 3 coolant sensors on the older (Renix) Jeeps. There is not one on the thermostat housing.

There is a SWITCH on the radiator, above the lower hose, that turns on the fan through a relay. The same relay turns the fan on when the A/C or defrost cycles when selected. The switch is the only thing that will trigger the relay, temperature wise.

The others have zero to do with turning on the e-fan. There is a SENDER on the back of the head, just for the gauge, only for the gauge.

There is a SENSOR on the block, below the manifolds, to tell the computer what's going on, and adjust air/fuel ratio. That's all it does.

So, if you replace your stock radiator and it doesn't have the bung for the SWITCH, you'll need to come up with a different switch set-up. Like one wired to the relay and inside the cabin. That one you'll be able to turn on manually, whenever you want. The relay will still turn the fan on when your A/C or defrost is on.
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Unread 04-19-2015, 11:43 AM   #4
Motorcharge
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I always forget 90 is Renix. 91-95 are as I described them regardless of the rear one being a sender rather than a sensor.
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Unread 04-20-2015, 09:38 AM   #5
seasoned_geek
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Originally Posted by Motorcharge View Post
1. Can you verify that it is actually overheating beyond simply seeing what the gauge reads? It's possible the sensor for the gauge is bad or that that portion of the instrument cluster isn't working properly anymore. Yes it's possible for it to overheat at idle regardless of the temperature outside, more or less.

2. It should kick on when the A/C compressor is on or at 210*. If it's not kicking on at 210 but does actually work the temp sensor for the computer may be bad.
Yes, it is actually overheating. I cannot generate temp readings for you now. The jeep is at my local mechanic. I'm too busy helping family with planting season to work on it myself.

Temp wise, it is 50/50 if the e-fan comes on. e-fan comes on 100% of the time with the A/C switch.
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Unread 04-20-2015, 09:46 AM   #6
seasoned_geek
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1990 XJ Cherokee 
 
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Quote:
Originally Posted by Paradise XJ View Post
There are actually 3 coolant sensors on the older (Renix) Jeeps. There is not one on the thermostat housing.

There is a SWITCH on the radiator, above the lower hose, that turns on the fan through a relay. The same relay turns the fan on when the A/C or defrost cycles when selected. The switch is the only thing that will trigger the relay, temperature wise.

The others have zero to do with turning on the e-fan. There is a SENDER on the back of the head, just for the gauge, only for the gauge.

There is a SENSOR on the block, below the manifolds, to tell the computer what's going on, and adjust air/fuel ratio. That's all it does.

So, if you replace your stock radiator and it doesn't have the bung for the SWITCH, you'll need to come up with a different switch set-up. Like one wired to the relay and inside the cabin. That one you'll be able to turn on manually, whenever you want. The relay will still turn the fan on when your A/C or defrost is on.
Thanks,

The radiator was replaced twice with factory stock as was the switch in the radiator.

I ordered a 3-core radiator which claims to be a drop in replacement with no required modifications. Sometimes you simply swat a mosquito with a cannon.

I _suspect_ this is a wiring issue due to age, corrosion or vermin. On a farm mice get into things from time to time. The reason I suspect wiring is the intermittent nature of the problem. Sometimes it comes on and sometimes it doesn't.

The only part of the cooling system which hasn't been replaced twice in the past year is the heater control valve and heater core. Other posts on here and other places are leading me to believe the heater control valve should be replaced to help lesson the heat issue.

http://www.cherokeeforum.com/f2/alum...-beware-16115/

The nice part about our old Jeeps is that a singular symptom is rarely a singular problem.
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Unread 05-07-2015, 01:11 PM   #7
seasoned_geek
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[SOLVED] 90 XJ electric fan not coming on all of the time

Picked the Jeep up from my "local" mechanic the other day. We did many many things. Put in a new 3-core radiator. Found and installed a new (and complete) fan shroud. Replaced the functioning fan clutch. It would still randomly overheat.

Here is the gist of the problem.

The better your mechanical fan cools the radiator, the more overheating problems you have.

I know that sounds counter intuitive, but it is true. The switch/sensor which controls the electrical fan is on the "cool" side of the radiator _after_ the mechanical fan has had a chance to work some magic. This is why when your fan clutch fails in the stuck-on mode, you overheat sitting in traffic.

I do not have the part number, but, O'Riely's (sp?) and probably other parts stores sell an after market electric fan thermal switch. It has a little thermometer type thing you stick in the fins of the radiator, adjustable on/off temperatures, etc. They used a bunch of the existing factory wiring circuit, but took the relay out from where it was. The new sensor+relay is all located on the electric fan side of the world. Yes, the A/C is still wired in.

Works like a charm.

That said, be ready for some slightly freaky behavior.

Most of us are used to turning the key to run and only hearing the fuel pump pressuring up. If the engine is cold, that is still all you hear. If you shut off hot, the fan kicks on.

In theory, we could have shopped around for months looking for switches to put in the factory location which had different on/off temps from stock and made things work. This was far less guess work.
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